Journal of Superhard Materials最新文献

Particular significance in the problems of the indirect analytical estimation of technological properties for grinding powders from synthetic diamond is substantiated for the spatial shape of grains. Referring to literature sources, it is pointed out that the actual 3D grain shape of such grinding powders, being used immediately instead of their 3D model, provides more reliable information about the values of technological properties. The creation of methodical tools for the automated 3D shape identification of a large-volume sample (up to 2000 grains) from such abrasive powders is emphasized to be of applied importance. An original method of solving such a problem for high-strength abrasive powders of synthetic diamond is proposed. The method is based on the known fact that grains of such powders are crystals with a 3D shape close to octahedra, cubooctahedra, and truncated octahedra. Some analytical and graphic information about the shape of an orthographic parallel projection of these spatial bodies is given depending on the 2D shape of the face, on which they are located. An analytical relationship between the geometric projection parameters required for the automatic identification of both the 2D shape of this projection and the 3D shape of grains and the generative parameters of an octahedron, cubooctahedron, and a truncated octahedron is derived. Some analogues to the morphometric characteristics of abrasive powders diagnosed by contemporary computer and technical tools with grains identical to the considered spatial bodies by their 3D shape are updated. The practical application of the developed methodical tools is illustrated by using high-strength abrasive powders AS250–AS500 from synthetic diamond as an example. It has been established that the relative content of grains shaped other than octahedra, cubooctahedra, and truncated octahedra is less than 31%.

The article investigated the introduction of nanomontmorillonite into vitrified bond, and the preparation of composite vitrified bond and vitrified bond diamond grinding wheels with different dosages of nanomontmorillonite by sol–gel method. The results show that the introduction of appropriate amount of nanomontmorillonite can effectively improve the comprehensive performance of vitrified bond diamond grinding wheels by utilizing its size effect and surface effect.

This article presents the results of preparing a starting powder system and compares two milling techniques based on surface area, impurity levels, and structural defectiveness. These factors are critical for fabricating high-thermal-conductivity AlN ceramic parts via pressureless sintering. The estimated quantities of gases adsorbed on the surfaces of both starting and milled AlN powders are also reported, providing essential data for designing technological routes to produce dense ceramic components of various sizes.

This article examines state-of-the-art research on diamond-abrasive machining of hard and brittle materials, with a focus on reproducing machining conditions at microscopic scales using high-resolution instruments. The discussion emphasizes the increasing utilization of porous, rough-surfaced, and nanotwinned (nt-D) diamonds. A new type of diamond with a rough surface, synthesized via thermochemical corrosion, exhibits a larger surface area and greater electronegativity than conventional diamond. These characteristics enhance interfacial adhesion between the binder and the diamond. Molecular dynamics simulations demonstrate their effectiveness in analyzing the mechanisms of abrasive processes such as nanocutting, grinding, and polishing. The findings identify critical grinding depth, vibration amplitude, and cutting speed as key machining parameters that determine the transition of diamond-abrasive machining of hard and brittle materials into a plastic regime. Recent publications recognize chemical–mechanical polishing as an efficient method for processing materials such as silicon carbide, monocrystalline silicon, nanotwinned diamond, and boron-doped diamonds [1].

The study reports the results of thermal conductivity measurements for WC–20 wt % Co and WC–20 wt % Ni alloys with a mesostructure, produced through free liquid-phase sintering. A comparison with literature data for alloys containing 20 wt % binder is also presented.

Theoretical models of elasticity and thermal conductivity have been developed for a polycrystal with imperfect grain boundaries and residual porosity. Based on the analysis of research data by these models, a quantitative estimate has been obtained for the thermal conductivity and elasticity of grain boundaries in polycrystalline cubic boron nitride, and the effect of the sintering temperature on them was studied. A strong dependence of macroscopic thermoelastic properties of a polycrystal on the state and properties of grain boundaries enables the application of the latter as a criterion of structural perfection in a polycrystal.

Diamond was synthesized in the Mg–Zn–C system under a pressure of 8 GPa and at a temperature of 1800°C. Following chemical purification, titanium was deposited onto the diamond powder grains via chemical vapor deposition. This study examined how the titanium coating affects the densification kinetics and microstructure of the resulting polycrystalline diamond composite. High-pressure sintering of the titanium-coated diamond powder decreased the temperature required for maximum densification by 300°C, compared with uncoated diamond powder.

This study investigates the feasibility of producing thick condensed TiC-based materials through high-rate electron-beam evaporation–condensation of graphite and titanium in vacuum. The research determines the dependences of density, porosity, and microhardness of both as-deposited and annealed condensates, subjected to a temperature of 1000°C, on the substrate temperature. The analysis of mechanical properties as a function of carbon content in TiC condensates demonstrates that the flexural strength reaches its maximum at a carbon concentration of 12–14 wt %, while microhardness peaks at 18–20 wt %.

Novel orthorhombic carbon allotropes with original topologies: 4⁴T39 C₁₂, mog-C₁₂ and cbs-C₁₆ were devised from crystal structure rationale of C4 tetrahedra stacking and connections backed by density functional theory DFT-based calculations of ground state structures and energy derived physical properties. Specifically, the structures were identified with distorted C4 tetrahedra versus perfect tetrahedra characterizing diamond, accompanied by small atom-averaged volumes resulting into high densities and subsequent ultra hard mechanical behaviors. Dynamically, the allotropes were found stable with positive frequencies revealed from their phonons represented in band structures. Pertaining thermodynamic properties showed specific heat C_V = f(T) calculated curves close to diamond’s experimental values from literature. The closest agreement with experiment was found for the most cohesive allotrope in the series, cbs-C₁₆, concomitantly with the largest electronic indirect band gap, like diamond. From the investigation, a holistic interrelationship: “crystal structure ↔ mechanical ↔ dynamic ↔ electronic properties” is deducted for carbon materials.

For the diamond grinding of ceramic silicon nitride balls based on a plane with circular feed under oscillation, some results of experimental study on the effect of the geometric parameters of the grinding process on the precision of their shape and the shape of the worn surface of a diamond wheel were reported. The shape accuracy criteria were the diameter variation and the out-of-roundness profile shape factor for ground balls and the radial slope angle of the working surface profile and the rate of change in this angle for the worn wheel surface shape. This effect was described by adequate linear functions of process parameters from the ratio between the quantities of balls on the circumferences of their location and the eccentricity of the location of a field of ball trajectories from the rotation axis of a diamond wheel under constant overlapping between the wheel rotation axis and the outer circumference, on which the balls were placed. The values of geometric parameters, at which the studied ball grinding scheme was reasonable to apply, were given.